1. Field of the Invention
This invention relates to a method of plumping (inflating) cut tobacco or pieces of finely cut tobacco leaves.
More particularly, it relates to a method of impregnating pieces of cut tobacco leaves with an adjuvant plumping agent (medium of inflation) such as carbon dioxide and subsequently forcing the adjuvant plumping agent to expand to consequently inflate the pieces of cut tobacco leaves, wherein means are provided to prevent shrinkage of the inflated tobacco and raise the extent of inflation of the final product.
2. Description of the Related Art
It has been a popular practice to impregnate pieces of dried and finely cut tobacco with an adjuvant plumping agent such as carbon dioxide under high pressure and at low temperature and subsequently exposing the cut tobacco impregnated with the plumping agent to a low pressure/high temperature atmosphere to force the adjuvant plumping agent to expand and consequently inflate the pieces of cut tobacco. The inflated pieces of cut tobacco are then appropriately mixed with unplumped cut tobacco and the blend of tobacco is wrapped by sheets of paper to produce cigarettes.
A blend of tobacco containing plumped pieces of cut tobacco offers a mild and agreeable taste. Besides, the amount of tobacco required for a cigarette can be reduced by using plumped tobacco to economize the consumption of tobacco leaves and lower the cost of cigarette production. Therefore, it is desirable to inflate pieces of cut tobacco as much as possible before they are used for cigarette production.
When plumped, cut tobacco loses its moisture and becomes very dry. Therefore, plumped cut tobacco is normally remoisturized (subjected to a moisture content regulating process) to contain moisture by 12 to 13% by weight, which is often referred to as standard moisture content. However, the remoisturized tobacco (that has undergone a moisture content regulating process) can easily shrink to partly or mostly lose the effect of a plumping process.
The extent of shrinkage of plumped cut tobacco during the moisture content regulating process can be minimized when the tobacco is exposed to a wet atmosphere having a specific humidity, e.g., a relative humidity of 60.degree. at 20.degree. C., so that it may gradually absorb the moisture in the atmosphere until a so-called equilibratory condition, where the percentage of moisture content of the tobacco is equalized with that of the atmosphere, is reached.
A moisture content regulating process as described above is, however, a lengthy one and may not commercially be feasible. Thus, a process as disclosed in Japanese Patent Publication Tokkou Shou Nos. 47-22800 and 49-1879 has been widely adopted in commercial cigarette production.
The process disclosed in these patent publications consists spraying a mist of very fine water drops onto plumped cut tobacco so that the tobacco may quickly absorb moisture. However, this process of accelerating the rate of moisture absorption of tobacco cannot satisfactorily resolve the problem of shrinkage and the degree of inflation of cut tobacco in the final cigarette product is inevitably limited.